This invention relates in general to an apparatus for the measurement of workpieces having possible interruptions in their surfaces. Specifically, this invention relates to the type of measuring apparatus having at least one moveable measuring rod wherein movement of the rod can be blocked, and in which the blocking of the measuring rod is controlled by at least one sensor such that the measuring rod is blocked when a surface interruption reaches the measuring rod and the blocking is lifted when the surface interruption leaves the area of the measuring rod.
This general type of measurement apparatus is known in the art. In West German DE-PS 960 861 there is described an apparatus that can be used for continuous or sectional surveillance of the dimensions of workpieces. In this apparatus two sensors are suspended on plate springs so as to move in a counterdirectional manner. Movement of the sensors can be blocked periodically during the measurement process by means of blades. The blocking of the sensors is controlled by means of a switch which is synchronized with the periodic interruptions in the surfaces of the workpieces in the appropriate manner. One drawback of this approach is that surface interruptions are not automatically sensed in that the time during which the sensor is blocked must, therefore, be determined in advance.
Another prior art device designed to prevent a measurement sensor from dropping into a grooved workpiece during processing is described in West German DE-OS 14 48 391. In this device sensor movement is blocked for much of the time and is a function of the selected blocking time. Sensor movement is unblocked automatically after some delay time after a surface interruption passes the sensor and then, after a predetermined time, sensor movement is again blocked. This device has the disadvantage that it can be used only with workpieces which have been measured beforehand. Furthermore, the blocking apparatus of this measurement device must be synchronized to the geometry and the angular speed of the workpiece.